Techniques for creating three-dimensional topographical data using a set of two stereoscopic photographs of the same spot taken from different viewpoints are known (for example, Patent Literature 1). More specifically, in such techniques, firstly, for each point in one photograph, its corresponding point presenting the same ground point is searched for in the other photograph of the stereoscopic pair. Then, the altitude of the point (altitude information) is calculated based on the parallax between the point in the first photograph and its corresponding point in the second photograph of the stereoscopic pair. The altitude (altitude information) is calculated for every point to create three-dimensional topographical data of the whole overlapping area shown in the stereoscopic pair.
Here, the corresponding point is searched for using, for example, the area correlation method in which for a point in one photograph, a point in the other photograph of the stereoscopic pair is identified as the corresponding point when their similarity level in terms of the surrounding luminance distribution and/or surrounding color distribution is equal to or higher than a given value.